I keep seeing windowed Fontana blocks for sale. Any theories why? Poor oiling, block flex, too much rpm, poor rod choice, or?

I have a buddy who let me take his car with an older Fontana to the Chilibowl a few years ago. Before I got it it had been windowed and rebuilt a few times. It had just been rebuilt with no laps on it when I took it. Made it through Monday hotlaps with no issues but it blew up at the end of practice on my qualifying night. Spit #1 rod out in the same spot it had been windowed and repaired before.

I had a good friend/good motor builder look it over to try to diagnose what the problem was. He was of the opinion that there was significant wear in the cam tunnel. That generation of Fontana didn't use any sort of roller bearing in the cam tunnel, and he decided that the wear was causing an oiling problem.

The owner had it rebuilt again, had some sort of modification done to install bearings in the cam tunnel, and the motor made it about 5-7 nights before it let go again. I don't know what all got replaced and what all got re-used in the last rebuild so it may have been another cam issue or it may have been a used part failure that time.

That motor has since been retired. A few bolt ons were robbed off of it to use on an ecotec with homemade injection and the owner is pleased as punch with what they are using now.